Semi-permanent hair coloration is an increasingly significant activity on a global basis, with the numbers of people using hair colorants, both in professional salons and in their own homes, increasing at a rapid rate. However, due to the chemical nature of many hair dyes, the users of these products are exposed to significant health risks, and there would be clear benefits for those who do apply hair colorants themselves, or undergo professional hair colouring treatments, in the development of alternative natural, non-toxic, non-carcinogenic products and application methods, which would minimise any potential hazards to human health.
Many commercial hair dyes are synthetically derived from petroleum feedstocks, and their manufacture frequently involves handling hazardous intermediates and the consumption of large volumes of petroleum based solvents. Furthermore, present hair coloration techniques typically involve the waste of up to 95% of the colour applied, which thereby is discharged to watercourses. Clearly, therefore, there would be considerable benefit in the development of biodegradable colorants, extracted from natural sources, and involving the use of benign technologies.
There has previously been interest in various colorants which occur in natural products, and one class that has received some attention is the group of polyphenols known as anthocyanins. Various prior art documents are available which teach the use of these materials in cosmetic products.
Thus, for example, PL-B-192692 teaches a method of obtaining anthocyanin dyes, and recovering the dyes from plant production wastes. Specifically, the patent discloses the extraction of anthocyanin dyes from coloured fruits, such as blueberry, black rose and black chokeberry, and their subsequent purification and use in food, cosmetic and pharmaceutical products. A specific method for pre-treatment of the fruit, and its extraction and subsequent purification by adsorption/desorption is provided. However, the authors offer no specific mention of other fruit sources, and neither is there any reference to the use of the product, or of any related formulation.
The website of a US cosmetic producer/supplier, Act by Nature LLC (http://actbynature.com/), advertises a variety of all-natural hair colorants, including “revolutionary patent pending natural permanent hair colour, colouring tints, and colour enhancing solutions made using 100% plant derived dyes”. However, limited technical information is provided regarding the nature of these dyes, although a general list of ingredients for hair dye formulations is available, and this list includes anthocyanins amongst the key ingredients. However, no further information is provided.
US-A-2006/246025 relates to natural fast-drying hair fixative compositions comprising polysaccharides, but is principally concerned with polysaccharide-based delivery systems comprising a combination of a linear polysaccharide such as pullulan and a monohydric alcohol, and includes no reference to any colouring system.
JP-A-62153211 is concerned with the use of anthocyanins in hair care products, and discloses hair preparations containing anthocyanins for dandruff control. However, it appears that the action of the disclosed anthocyanin ingredients is specifically in the control of dandruff in the disclosed hair tonics, since no mention is made of dyeing activity. Specific anthocyanin structures (I) are disclosed, although the document is silent regarding source fruit and methods of extraction and purification.

The disclosed hair preparations for control of dandruff contain at least one compound selected from anthocyanins (I) (wherein R1 and R2 are independently H, OH, or MeO; R3 and R4 are independently H or β-glucoside). Polyoxyethylene oleyl alcohol ether, delphinidin and a fragrance are added to ethanol and the alcoholic phase is added to water containing glycerine to give a hair tonic.
U.S. Pat. No. 6,620,410 teaches hair care compositions which are designed to provide increased protection from ultraviolet radiation. The disclosed formulations comprise grape skin extract, and are alleged to display anti-UV radiation properties. It is believed that the grape skin extract will inevitably contain anthocyanins, although the document contains no specific disclosure of anthocyanins, or of any other anthocyanin sources; in addition, the patent fails to teach or suggest the use of any extract for the purposes of hair coloration.
U.S. Pat. No. 6,241,785 relates to flavyllium-type compounds and their use in dyeing keratinous fibres, with particular emphasis on human hair. These derivatives are members of a chemical class to which anthocyanins belong. However, the disclosed compounds are obtained synthetically, and not via the extraction of fruit. Furthermore, the patent specifies compounds (II) having particular substitution patterns, thereby excluding anthocyanins.

JP-A-4119179 teaches a specific anthocyanin compound—cyanidin 3-O-arabinoside—for use in dyeing wool in combination with quercetin glucouronide. However, whilst the document teaches formulation of the dye, no information is provided with regard to the source of the anthocyanin, or its recovery. Furthermore, the patent concerns the dyeing of a fibre, with specific mention being made of silk and wool, and requires dyeing conditions of pH≦2.5 combined with a temperature 95° C. for 1 hour, conditions which would be wholly inappropriate for dyeing human hair. Despite its proposed use as a dye, the document makes no mention of the application of the material to hair, or indeed its use in any cosmetic application.
US-A-2007/0251024 teaches the application of natural colorants to hair in a process requiring the inclusion of a mordanting agent, such as a mineral or metal salt, in the hair dyeing process. The inventors describe the inclusion of the mordant to provide substantivity between the dye and hair fibre, inferring that in the absence of the mordant dyeing would not be possible as the limited affinity of the dyes would not allow sufficient build-up of colour on the hair fibre. The claimed invention is, in many ways, analogous to centuries-old wool dyeing processes which require application of natural dyes with a mordant. However, the document contains no suggestion of the application of natural polyphenols as dyes without a mordant.
The literature provides few examples relating to the dyeing of textile fibres with anthocyanin based dyes, although there have been recent reports of the successful application of an aqueous extract of grape pomace to dye cotton pre-mordanted with tannins, and bleached wool yarn, in each case yielding red/violet shades. The dyeings in this study were conducted by exhaustion methods, employing aqueous dyebaths with or without metal salt (or tannin) mordant added to the solution.
The increasing demand for dyes for use in the dyeing of human hair which are free from potential health hazards has presented an opportunity for manufacturers to exploit dyes such as anthocyanins, which are available from natural sources via clean technologies, for such purposes. However, there is at present no satisfactory commercial process for the production of dyes in this way. The present inventors have, therefore, investigated the production of colorants from natural sources, and have developed a range of natural compounds, and methods for their production, which facilitate the production of safe, commercially viable, hair dyes.